diff --git a/pkgs/build-support/rust/fetch-cargo-tarball/default.nix b/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
index 96db232ce2f53..53a332bff2423 100644
--- a/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
+++ b/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
@@ -136,7 +136,7 @@ stdenv.mkDerivation (
 
       # Packages with git dependencies generate non-default cargo configs, so
       # always install it rather than trying to write a standard default template.
-      install -D $CARGO_CONFIG $name/.cargo/config
+      install -D $CARGO_CONFIG $name/.cargo/config.toml
 
       runHook postBuild
     '';